On the back of the cornea of a human eyeball, there is a cellular film called an endothelial cell which consists of tortoise shell-shaped cells having a size of about 20 microns and which plays the most important role in maintaining the transparency of the cornea. Hence, it is believed to be of the utmost importance to observe and photograph the endothelial cell in vivo. In performing the transplantation of the cornea, for example, it is important to know the conditions of the endothelial cell of the cornea to be transplanted. It is also important to observe the corneal endothelial cell in order to confirm the results of the surgical operation after the transplantation. The observation and examination of the corneal endothelial cell is also necessary to determine the influence of an instrument or an artificial lens on the cell when they are inserted into the eyeball in performing a surgical operation on a cataract.
The endothelial cell film of the cornea is as transparent as the corneal substrate and the contrast with its surroundings is so weak that observation with an ordinary microscope is rather difficult. For this reason, a specific illumination method has been employed. In other words, a thin slit luminous flux is used for illumination and the optical axis of illumination must be arranged at a suitable angle relative to the optical axis for observation and photography lest the reflected ray of light on the corneal surface enter the photographing system.
Conventional apparatuses produced for this purpose are broadly classified into two groups. One is the type in which the illumination system and the observation and photographing system use an objective lens in common, and the other in which both systems have respective separate objective lenses. In any case, magnification of at least about 100 times is necessary for the observation of the corneal endothelial cell and magnification of about 20 times is necessary for taking a photograph. For this reason, the conventional apparatuses have been produced exclusively for the purpose of observing and photographing the endothelial cell of the cornea, and they are expensive and call for a high level skill for their operation.